Segal, R. A. | bioRxiv Science

bioRxiv2020

Fast transport of RNA granules by direct interactions with KIF5A/KLC1 motors prevents axon degeneration

Complex neural circuitry requires stable connections formed by lengthy axons. To maintain these functional circuits, fast transport delivers RNAs to distal axons where they undergo local translation. However, the mechanism that enables long distance transport of non-membrane enclosed organelles such as RNA granules is not known. Here we demonstrate that a complex containing RNA and the RNA-binding protein (RBP) SFPQ interacts directly with a tetrameric kinesin containing the adaptor KLC1 and the motor KIF5A. We show that binding of SFPQ to KIF5A/KLC1 motor complex is required for axon survival and is impacted by KIF5A mutations that cause Charcot-Marie-Tooth (CMT) Disease. Moreover, therapeutic approaches that bypass the need for local translation of SFPQ-bound proteins prevent axon degeneration in CMT models. Collectively, these observations show that non-membrane enclosed organelles can move autonomously and that replacing axonally translated proteins provides a therapeutic approach to axonal degenerative disorders.

cell biology↗

bioRxiv2019

The Eya1 phosphatase mediates Shh-driven symmetric cell division of cerebellar granule cell precursors

During neural development, stem and precursor cells can divide either symmetrically or asymmetrically. The transition between symmetric and asymmetric cell divisions is a major determinant of precursor cell expansion and neural differentiation, but the underlying mechanisms that regulate this transition are not well understood. Here, we identify the Sonic hedgehog (Shh) pathway as a critical determinant regulating the mode of division of cerebellar granule cell precursors (GCPs). Using partial gain and loss of function mutations within the Shh pathway, we show that pathway activation determines spindle orientation of GCPs, and that mitotic spindle orientation directly correlates with the mode of division. Mechanistically, we show that the phosphatase Eya1 is essential for implementing Shh-dependent GCP spindle orientation. We identify atypical protein kinase C (aPKC) as a direct target of Eya1 activity and show that Eya1 dephosphorylates Threonine (T410) in the activation loop of this polarity complex component. Thus, Eya1 inactivates the cell polarity complex, resulting in reduced phosphorylation of Numb and other components that regulate the mode of division. This Eya1-dependent cascade is critical in linking spindle orientation, cell cycle exit and terminal differentiation. Together these findings demonstrate that a Shh-Eya1 regulatory axis selectively promotes symmetric cell divisions during cerebellar development by coordinating spindle orientation and cell fate determinants.\n\nSummary statementBiological responses to Shh signaling are specified by the magnitude of pathway activation and the cellular context. This study shows that potent Shh signaling regulates mitotic orientation and symmetric division of cerebellar granule cell precursors in a process that requires the phosphatase Eya1 and unequal distribution of cell fate determinants to daughter cells.

neuroscience↗